The present invention generally relates to an air conditioner, and particularly relates to a circuit for properly controlling an inverter to thereby control the capacity of a compressor in an air conditioner in accordance with the operation state of the air conditioner, whether the air conditioner is operated as a cooler or a heater.
As disclosed, for example, in U.S. Pat. No. 4,257,238, the capability of a compressor can be smoothly and continuously changed in accordance with an indoor air conditioning load by controlling an inverter circuit which drives a compressor motor. In the case of using such an inverter circuit as described above, generally, control is performed such that a current flowing in the inverter circuit is detected and a rotational speed of a compressor motor is reduced when the detected current exceeds a predetermined value, called as a limit current value. Semiconductor devices are used in such an inverter circuit, and it is known to reduce, generally, the rating of the semiconductor devices and the rate of derating varies in dependent of the ambient temperature. In the conventional inverter control circuit, however, no consideration has been given to the efficient use of an inverter circuit in accordance with the ambient temperature.